Method of manufacturing a solid-state imaging device

Abstract

A frame transfer-type solid imaging device is provided, which can be operated without reducing the transfer efficiency or the transfer charge quantity. A plurality of N-type regions 5 constituting photoelectric conversion regions and a plurality of P+-type regions 6 constituting channel stop regions are formed on a P-type silicon substrate 4, and a transparent electrode 1 is further formed through an insulating film 7 on the substrate 4. The thickness of the transparent electrode at a portion above the photoelectric conversion region is made thinner than the thickness of the other part of the transparent electrode 1, and an antireflection film 8 is formed above the photoelectric conversion region 2.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a solid imaging device and a method of manufacturing the same, and particularly relates to a frame transfer or a full frame transfer-type solid imaging device, which is provided with the improved sensitivity and resolution without reducing the transfer efficiency or the transfer charge.2. Background ArtWhen CCD type solid imaging devices are classified by their operation mode, there are two systems: one is an interline transfer system and another one is a frame transfer system (or a full-frame transfer system). In the solid imaging device operated by the interline transfer system, each pixel is constructed by a PN junction, and light is incident on the N-type region through the insulating film formed on the region. A vertical CCD resistor is formed adjacent to each pixel in sequence, and the signal charge accumulated on the light receiving portion is transferred to the vertical CCD resistor. The con...

AI Technical Summary

Benefits of technology

It is therefore an object of the present invention to provide a frame transfer-type or a full frame transfer-type solid imaging device and method of manufacturing the same, which is superior in sensitivity or resolution without reducing the transfer efficiency or the transfer charge quantity.

According to the solid imaging device of the present invention, since an antireflection is disposed on a part of the surface of the transparent electrode located at a position above the photoelectric conversion region, the quantity of light arriving to the photoelectric conversion region through the transparent electrode and the insulating film increases; that is, the transmission increases. As a result, the sensitivity is improved. Furthermore, it is possible to prevent total reflection of light when an antireflection film having an intermediate refractive index between that of the transparent electrode and the second insulating film is used.

In addition to adopting the antireflection film, when a part of the transparent electrode corresponding to the photoelectric conversion region is made thinner than the other part, the light transmission increases, which results in improving the sensitivity. In other words, since the portion of the thickness of the transparent electrode excluding the area corresponding to the photoelectric conversion region is thick in the present invention, the wiring resistance can be reduced when compared to the conventional device, in which the transparent electrode is formed into a uniformly thin film for the sake of transmission. Consequently, it is possible to prevent the read pulse from rounding and to prevent reduction of the transfer efficiency and the transfer charge quantity. In this case, it is necessary to reduce the thickness of the transparent electrode corresponding to the photoelectric conversion region to less than 300 nm, and it is preferable that the thickness is in a range of 150 to 200 nm. If too thick, the low transmission degrades the sensitivity. There is a proportional relationship between the film thickness and the area of the light receiving cell, and if the cell area is constant, the sensitivity increases with decreasing thickness, and if the sensitivity is constant, the cell area may decrease.

When a light shielding film is formed on, for example, the channel stop regions, the light incident to the channel stop regions is shielded. Thus, the resolution of the device is improved because the light incident to a photoelectric conversion region is prevented from being incident to the adjacent photoelectric conversion region.

By the use of the manufacturing method of the present invention, it is possible to manufacture the solid imaging device which is superior in sensitivity or the resolution without reducing the transfer efficiency and the transfer charge quantity. When a solid imaging device is manufactured, which comprises features of (1) having a thin part of the transparent film formed above the photoelectric conversion region, (2) having a antireflection film formed on the transparent electrode above the photoelectric conversion region, and (3) having a light shielding film formed on the transparent electrode excluding the area above the photoelectric conversion region, these features can be manufactured in sequence in the order (1), (2) and (3). The order can be changed to the order (1), (3) and (2).

Problems solved by technology

However, several problems have been encountered in the conventional solid imaging device: the sensitivity is reduced when the transparent film is thick, and the transfer efficiency and the quantity of the transfer charge are reduced when the transparent film is thin.

The resolution of the conventional imaging device is also not satisfactory.

However, when the thickness of the transparent film is increased, a part of the light incident to the transparent film is diffused, and the transparency of the transparent electrode decreases so that the sensitivity of the imaging device is reduced.

If the thin transparent electrode is used in order to increase the sensitivity, the wiring resistance increases, which results in causing a problem of the pulse rounding, and in decreasing the transfer efficiency and the transfer charge quantity.

Furthermore, when the structure shown in FIG. 7 is considered, light incident to the periphery of the channel stop region through the transparent electrode is distributed to both of the photoelectric conversion regions of the channel stop region to cause photoelectric conversion, which results in the reduction of the resolution of the imaging device.

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